zoukankan      html  css  js  c++  java
  • IMP self _cmd

    The only way to circumvent dynamic binding is to get the address of a method and call it directly as if it were a function. This might be appropriate on the rare occasions when a particular method will be performed many times in succession and you want to avoid the overhead of messaging each time the method is performed.

    With a method defined in the NSObject class, methodForSelector:, you can ask for a pointer to the procedure that implements a method, then use the pointer to call the procedure. The pointer that methodForSelector: returns must be carefully cast to the proper function type. Both return and argument types should be included in the cast.

    The example below shows how the procedure that implements the setFilled: method might be called:

    void (*setter)(id, SEL, BOOL);
    int i;
     
    setter = (void (*)(id, SEL, BOOL))[target
        methodForSelector:@selector(setFilled:)];
    for ( i = 0 ; i < 1000 ; i++ )
        setter(targetList[i], @selector(setFilled:), YES);

    The first two arguments passed to the procedure are the receiving object (self) and the method selector (_cmd). These arguments are hidden in method syntax but must be made explicit when the method is called as a function.

    Using methodForSelector: to circumvent dynamic binding saves most of the time required by messaging. However, the savings will be significant only where a particular message is repeated many times, as in the for loop shown above.

    Note that methodForSelector: is provided by the Cocoa runtime system; it’s not a feature of the Objective-C language itself.

  • 相关阅读:
    Vue学习笔记(4)-带参数路由,嵌套路由,编程式导航
    JS数组&&数组对象去重
    Vue学习笔记(3)-品牌管理系统
    Vue学习笔记(2)-组件生命周期
    负margin
    CSS布局奇淫巧计之-强大的负边距
    由浅入深漫谈margin属性
    双飞翼布局和圣杯布局的对比
    圣杯布局的实现过程
    CSS实现垂直居中的5种方法
  • 原文地址:https://www.cnblogs.com/feng9exe/p/7131445.html
Copyright © 2011-2022 走看看